This invention relates to fluid--fluid contacting apparatus and, in particular, to structured packings for use in such apparatus. Typically apparatus of the type that the invention relates to is used for operations such as distillation, absorption, scrubbing, stripping, heat exchange etc. in which one fluid (e.g. a liquid) is brought into contact with another fluid (e.g. a gas) with the fluids usually flowing countercurrent relative to each other. In the case of gas (or vapor)/liquid contacting, the gas constitutes the continuous phase.
The invention is especially concerned with fluid--fluid contacting apparatus in which the structured packing comprises a number of packing elements arranged in succession in the direction of fluid flow through the apparatus which is usually in the form of a vertically disposed column or tower. Each packing element comprises a plurality of crimped sheets of material arranged in face-to-face relationship with rectilinear corrugations extending obliquely relative to the direction of fluid flow and successive elements are arranged with the sheets in one element angularly displaced with respect to the sheets of the adjacent element(s). Vendors of commercially available packings of this type recommend angular displacements of 90.degree. (Sulzer Brothers Limited) and 70.degree. (Norton Chemical Company).
In their range of packings, one supplier (Sulzer) produces an `X` range of packings and a `Y` range of packings. The sheet materials used in the two forms of packings are believed to be identical with respect to surface area and surface treatment but differ by the angle of crimp. In the `Y` series of packings, the crimp angle is 45.degree. to the horizontal whereas the `X` series have a crimp angle at 60.degree. to the horizontal.
The `Y` series packing elements have a higher efficiency but lower capacity than the `X` series packing elements. The efficiency of a structured packing is a property of the way vapor and liquid contact each other over the whole surface of the packing. The capacity of the packing is set by the capacity at its most restricted elevation. The `X` series packing elements impose a smaller change in direction on the fluids at the interface due to the larger angle subtended to the horizontal by the crimp angle and therefore have a larger capacity than the equivalent `Y` series packing elements. The pressure drop within the `Y` series packing elements is greater and the use of the surface area for mass transfer is greater, hence the `Y` series packing elements have a higher efficiency.